[There's more to Lexx than that (although that's definitely part of it). It's best episodes are bizarre surreal farces - a character playing a game of chess with a Death-like antagonist, the cast being compelled to sing in a musical about the undead character's living days. At it's worst, Lexx is the worst TV show I've willingly sat through, but in its better hours, it was pretty fun.
But to answer the OP's question, Babylon 5 is a better purchase. Lexx has it's moments, but it's wildly uneven and it's probably too weird and/or too filthy or too often terrible for most viewers. And even then, when it comes to outre space opera, Farscape is by far the better series
That's a pretty good summation for me. Although in the end I went with both, having skipped on broadcast TV for releases on DVD/streaming, why not enjoy both.